1. Field of the Invention
The present invention refers to an apparatus for controlling the data traffic in a cell of a cellular network. The invention is further directed to a method for measuring the Quality of Experience of an ongoing data session in a communication system comprising client and server devices which are interconnected over a packet-switching data link. Furthermore, the invention is related to a video server for providing at least two video streams.
2. Description of Related Art
In today's mobile data networks, data streaming accounts for a major part of transmitted data volume which is expected to increase in the near future. In particular, applications which are based on video streaming enjoy increasing popularity. Typical services provide several video streams which are provided by designated video servers. Users can establish data sessions to said servers in order to play video streams at their specific client devices. However, these data sessions often require a higher bandwidth than voice services or other data services.
The increasing demand for streaming data, in particular video streaming, poses a great challenge to future network management. The quality of the offered streaming services often depends on the available data rate allocated to each subscriber by the network management. As the Internet and today's mobile data networks do not guarantee bitrates for the individual application, it can always happen that throughput is limited by network constraints down to a level which does not allow to transmit the video signals according to the playing rate which causes stalls of the video being watched by the user.
Therefore, one major function of network management is to assure a sufficient Quality of Experience, in the following referred to as QoE, of said streaming services. For example in voice or video applications the QoE stands for an available voice or video image quality. Hence, reliable measurement methods for live network data streaming are key parts of QoE measurements especially for mobile data applications.
A first intuitive approach could be to measure the perceived bandwidth of the individual video stream and compare this with the bandwidth required by the streaming application. This approach however lacks in precision: modern video codecs such as H.264 use variable bitrates coding so the actual bandwidth demand can only be estimated.
As is known from the prior art, Quality of Service, in the following referred to as QoS, standards provide methods for bandwidth allocation and service prioritisation. However, in current mobile cellular networks it is required to define these QoS parameters before establishing data sessions, in particular streaming sessions. Normally, these parameters are set in specified header fields of the used data packets. Changes of said parameters during live-network traffic are prohibited. Moreover, these parameters must be configured manually on the client device. Even if a mobile network would consider these QoS settings, they do not apply end-to-end, i.e. they may only apply for the air interface of a mobile network and not for the backbone or the part of the route in the Internet.